1. Field of the Invention
The present invention relates to a display device and a method for manufacturing the display device. The present invention also relates to an electronic appliance having a display panel using the display device.
2. Description of the Related Art
In recent years, as display devices such as liquid crystal display devices and electroluminescent display devices (hereinafter referred to as EL display devices), display devices each having the structure (hereinafter referred to as a system-on-panel type) in which a display portion including a pixel portion and a driver circuit for driving the pixel portion, a circuit group (hereinafter referred to as a peripheral circuit portion) provided for operating the display portion, such as an arithmetic circuit or a memory circuit, are formed over one substrate have been known. In each of these system-on-panel display devices, as transistors included in circuits of a display portion and a peripheral circuit portion, transistors using polycrystalline semiconductor materials for semiconductor layers have been known, for example.
A polycrystalline semiconductor material has higher field effect mobility than an amorphous semiconductor material such as amorphous silicon. Further, with a polycrystalline semiconductor material, not only an n-channel transistor but a p-channel transistor can be formed. Thus, with a polycrystalline semiconductor material, a CMOS circuit can be formed and a polycrystalline semiconductor material is more preferably applied to not only a semiconductor layer of a transistor included in a circuit in a display portion but a semiconductor layer of a transistor included in a circuit required to be operated at high speed, such as an arithmetic circuit, in a peripheral circuit portion, than an amorphous semiconductor material.
As an example of a display device in which a display portion and a peripheral circuit portion are formed over one substrate with the use of such a polycrystalline semiconductor material, Patent Document 1 (Japanese Published Patent Application No. 2004-146082) and the like are given. Patent Document 1 discloses an example of an EL display device in which a display portion, an arithmetic circuit for a peripheral circuit portion, and a booster circuit are formed over one substrate.